This invention relates to automotive vehicle engine valves, and in particular to a bearing disposed within an exhaust gas recirculation (EGR) valve for supporting a reciprocating valve shaft.
It is known in the art relating to automotive vehicle engines to provide selective recirculation of engine exhaust gases into the intake manifold in order to control exhaust emissions. To this end, an exhaust gas recirculation (EGR). valve may be provided which includes a valve assembly connectable with associated intake and exhaust manifolds or systems of the engine to meter the flow of exhaust gas from the intake to the exhaust.
EGR valves typically include a valve assembly operable to close or open a passage between the intake and exhaust manifolds. The valve assembly includes a valve member (or pintle) having a head connected with a shaft supported by a bearing for reciprocating motion within a valve body. An actuator assembly is operably connected with the valve assembly and includes a solenoid coil and an armature connectable with the valve member. The solenoid coil actuates the armature to open the EGR valve, which, in turn, is closed by a spring when the coil is deenergized.
To minimize leakage of exhaust gas into the valve assembly and/or the solenoid. actuator, the diametral clearance between the valve shaft and its bearing is very tight, in the range of xc2x10.03 mm or less.
To maximize lubricity between the reciprocating shaft and its supporting bearing, the shaft and the bearing may be composed of different materials (e.g. stainless steel and sintered brass, respectively). Typically, these materials have very different thermal properties. Because EGR valves and their components are exposed to extreme operating temperatures (xe2x88x9240xc2x0 C. to 700xc2x0 C.) and radical temperature changes, a valve shaft may ultimately seize within its bearing as a direct result of differential thermal expansion of the bearing and shaft. The tendency of the shaft to seize is exacerbated by the fact that a bearing is often press fit into a valve body along its exterior surface, and, upon undergoing dramatic changes in temperature, tends to expand inwardly toward the outer surface of the shaft, rendering the valve inoperable.
It is therefore desirable to provide a valve with a bearing assembly adapted to guide the valve, shaft as it reciprocates through the valve body, and which is self-compensating when subjected to extreme temperature changes such that thermal expansion of the shaft/bearing does not interfere with valve actuation.
The present invention provides a valve including a self-compensating bearing assembly including a rigid bearing member for guiding the valve shaft as it reciprocates through the valve body and a pliant annulus surrounding the valve shaft having a density and thickness sufficient to accommodate distortion of the rigid bearing member in response to changes in temperature without interfering with shaft actuation.
The pliant annulus has multiple degrees of freedom and its pliancy can be varied depending on its material composition. For example, the pliant annulus may be a woven metal mesh core, the pliancy of which is determinable by the filament size and weave density.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.